In the case that a moving image transmission apparatus uses a network whose network bandwidth is not secured sufficiently for providing the internet service and the mobile communication service, an available network bandwidth of the moving image transmission apparatus becomes unstable due to various causes. There is a moving image transmission apparatus to transmit contents, such as a moving image, which require high level throughput continuously, through the network. The moving image transmission apparatus suffers from frequent stop of playing back the contents due to shortage of the network bandwidth. Hereinafter, it is defined that the moving image includes any one or both of a moving picture and a voice.
As one of general methods to solve the above-mentioned problem in this field, there is a method that the moving image transmission apparatus carries out data compensation for a packet loss by use of Forward Error Correction (FEC) which has a fixed redundancy. In the case that characteristics of the network, which is used for transmitting the moving image, is known in advance, it is possible to compensate the data in real time with a simple method of using FEC. However, in the case that many packet losses exceeding a packet loss rate which is estimated, in advance, on the basis of the network characteristics are caused, the moving image transmission apparatus can not compensate the lost packet. Accordingly, the moving image transmission apparatus has a defect that it is difficult to use FEC in the network whose available bandwidth is changed significantly. In order to avoid the problem, the moving image transmission apparatus assigns firstly large redundancy to data related to a service, and then provides the service. In this case, the moving image transmission apparatus transmits the packet excessively even in a state that the network has almost no problem. Accordingly, the moving image transmission apparatus consumes the network bandwidth more than necessity.
As another general method to solve the above-mentioned problem in this field, there is a method that a moving image receiving apparatus requests to re-send lost data and the moving image transmission apparatus re-sends the requested data to improve immunity against the packet loss. In the case that the method is used, the moving image transmission apparatus has an advantage that the network bandwidth, which is required for re-sending the data, is narrow, since the moving image transmission apparatus re-sends only the lost data. However, in the case that the method is used, it takes the following time for re-sending the data, that is, a time until the moving image transmission apparatus recognizes that the packet loss is caused, a time requisite to requesting to resend the data, and a time requisite to re-sending the lost data. Accordingly, in the case that the method is used, long latency is caused in an interval from transmitting the data firstly until regenerating the data. As a result, a defect that the real-time characteristic is lost is caused.
As a method, which remedies the defect of FEC, out of the above-mentioned methods, a method denoted as Adaptive FEC is proposed in a non-patent literature (NPL) 1. The moving image transmission apparatus, which uses the Adaptive FEC, changes the redundancy dynamically so as to minimize the packet loss. Accordingly, it is possible that the moving image transmission apparatus restrains the packet loss even if the moving image transmission apparatus communicates through the network whose available bandwidth is changed to some extent. Moreover, in the case that the network is in a good state, it is possible that the moving image transmission apparatus transfers the moving image with making the redundancy not so large. As a result, it is possible to reduce an ineffective use of the network bandwidth.
However, according to the method described in the non-patent literature 1, the moving image transmission apparatus makes the redundancy large in the case that the network enters into a bad state. For this reason, the moving image transmission apparatus transmits and receives excessively the packets which include an amount of data corresponding to the redundancy. Therefore, according to the method described in the non-patent literature 1, there is a possibility that the moving image transmission apparatus falls into a bad cycle of making the network state degraded furthermore. As a method to improve the problem, there is a method which is described in a patent literature 1. According to the patent literature (PTL) 1, the moving image transmission apparatus reduces packets which carry data of the moving image, and determines an encoding bit rate of the moving image so that a bandwidth, which is corresponding to a total number of packets including the data of the moving image and packets including redundancy data of FEC, may be narrower than the network bandwidth. As a result, it is possible that the moving image transmission apparatus obtains the best quality of the moving image without degrading the network quality.
According to further another method described in a patent literature (PTL) 2, in a situation that the network state becomes degraded, the moving image transmission apparatus carries out transmitting and receiving the packet with giving priority to the packet carrying the moving image, and restrains to transmit the packet based on FEC. As a result, even if the network state becomes degraded abruptly, the moving image transmission apparatus can prevent that the network state becomes degraded furthermore due to the packet which the moving image transmission apparatus transmits and receives.